1. Field of the Invention
This invention relates generally to an apparatus for driving a piston, and particularly to a piston driving apparatus, such as an engine-powered nailer, utilizing the fuel combustion energy.
2. Prior Art
One example of a conventional piston driving apparatus is disclosed in U.S. Pat. No. 4403722 as a combustion gas-powered fastener driving tool. In an embodiment of the disclosed tool, a piston is reciprocally moved up and down in a cylinder by a pressure originated by the combustion of fuel gas, and a combusted gas is exhausted from a port which is provided between the top dead point and the bottom dead point after the piston passes the port in a compression stroke. The combustion of the gas advances from an ignition plug to the upper surface of the piston. In this structure, however, since an unburned gas following the piston movement is firstly exhausted at the upper surface of the piston from the port, the fuel consumption rate is high. In addition, such an exhausted unburned gas is in danger of explosion when this tool is used at a badly ventilated place.